Water to be fed to a power-plant condenser is generally passed through a filter adapted to remove solid particles therefrom. It is customary to provide the filter with a generally cylindrical filter housing having fittings for feeding the water generally radially into the unit and recovering the filtered water generally axially therefrom. Within the filter housing there is provided a substantially cylindrical filter basket which traps the solid particles which may be entrained by the liquid.
In conventional apparatus of this type (see, for example, German Patent Dt-PS 20 58 395), the filter basket comprises filter-basket rings having their peripheries connected contiguously together, e.g. welded together.
The rings thus form, within the limits of precision and the tolerances of fabricating the rings, a cylindrical shell of the filter basket conforming to a right circular cylinder. Stiffening is provided by a three-dimensional frame construction of ring elements and rods whose parts are secured together by welding and/or bolting to the shell.
This construction has been found to be expensive in practice and investigations have shown that it has several drawbacks.
Firstly, during the formation of the filterbasket rings from a flat perforated plate or strip, which is stamped with generally cylindrical holes, the perforations, after bending, tend to decrease in diameter from the exterior toward the interior, i.e. in the flow direction. The result of this generally conical convergence of the perforations is that it permits particles to be trapped in a selflocking manner, thereby rendering it difficult to remove the solids during cleaning of the filter.
Secondly, the stability of the shell depends upon the thickness of the sheet metal from which it is formed. However, since an increase in thickness also means a corresponding increase in the covergence of the walls of the perforations, the construction of the conventional units must be a compromise between the desire to maintain the wall as thin as possible and a need to provide a thick wall to resist oscillation and vibration phenomena which develop within the filter. Such phenomena can cause fatigue of the material of the shell and eventual rupture thereof.
Thirdly, while the vibration phenomena and the tendency toward material fatigue of the shell can be counteracted by a corresponding configuration of the stiffening structure, the elements forming the stiffening means tend to disrupt the turbulent flow of the liquid traversing the filter basket because the components of the stiffening structure do not lie generally along the flow lines of the turbulent stream. As a result, the pressure loss is high and it is difficult to effectively clean the filter, i.e. to carry off the accumulated solids during the backwashing or other cleaning operation.